This invention relates to a method for detecting/processing color image information which is capable of precisely and automatically detecting the image information in color registration on a color original film without positional adjustment of image sensors even if the sensors are provided separately for each of plural colors.
In a photograhic printing system, it is necessary to photometrically measure the density of an original film (i.e. a film negative formed by developing a film negative) to determine its exposure amount or correction amount for printing. The density of the film negative is conventionally measured in LATD (Large Area Transmittance Density) with photosensors such as photodiodes provided near the optical path of a printing optical system. However, since the LATD image detection is a method for measuring the average density of the film negative in average but not for accurately measuring it across a frame, the printing exposure or correction is not quite precisely determined.
FIG. 1 shows a system which is proposed by this applicant to solve such problems encountered in the prior art.
A film negative 2 is conveyed by a conveying mechanism 9 to a position on a film negative carrier 1. The film negative 2 is illuminated with the light from a light source 4 via a color compensation means 3 which comprises 3 color filters of yellow (Y), magenta (M) and cyan (C). The light transmitted through the film negative 2 is directed to reach a photographic paper 7 via a lens unit 5 and a black shutter 6. The photographic paper 7 is wound around a supply reel 7A and reeled on a take-up reel 7B in synchronism with the movement and suspension of movement of the film negative 2. Photosensors 8 such as photodiodes are provided near the lens unit 5 of the film negative 2 in order to detect image density information of the three primary colors. Utilizing the detection signals from such photosensors 8, picture printing is carried out. An image information detecting apparatus 10 comprising a two-dimensional image sensor 11 is operatively positioned near the film negative 2 at a position inclined from an optical axis LS of the light source 4 and the film negative 2. A lens unit 12 is provided in front of the two-dimensional image sensor 11 to substantially focus the center area of the film negative 2. On the back of the image information detecting apparatus 10 is attached a substrate board 13 for mounting a processing circuit comprising integrated circuits and so on.
The two-dimensional image sensor 11 comprises, as shown in FIG. 2, an image pickup section 101 for optically picking up an image, a storage section 102 for storing charges transmitted from the image pickup section 101, and an output register 103 for outputting the charges stored in the storage section 102. By controlling driving signals 101S through 103S from a driving circuit, the image information in two-dimensions (area) is photo-electrically converted and outputted serially from the output register 103 in the form of an analog image signal PS. The circuit mounted on the substrate board 13 has, for example, a circuit structure shown in FIG. 3. The image sensor 11 is driven by driving signals 101S through 103S supplied from the driving circuit 20. The light illuminating the image pickup section 101 of the image sensor 11 is outputted from the output register 103 as a picture signal PS, sampled and held by a sample-and-hold circuit 21 at a predetermined sampling cycle. The sample value thereof is converted by an analog-to-digital (A/D) converter 22 into digital signals DS. The digital signals DS from the A/D converter 22 are inputted into a logarithmic converter 23 for logarithmic conversion, then converted to density signals DN, passed through a write-in control circuit 24 and finally written in a memory 25.
A reading speed signal RS from the driving circuit 20 is inputted into the write-in control circuit 24 in order to read out image information at a predetermined speed when the image sensor 11 is driven. The write-in control circuit 24 writes in the density signals DN at predetermined positions of a memory sequentially and corresponding with the driving speed (i.e.--the scanning speed across the face thereof) of the image sensor 11. In other words, the reading speed of the image sensor 11 is determined by the driving speed. The reading speed in turn determines the segmentation number of picture elements with respect to an image area. The memory 25 should therefore store the detected information in correspondence with the number of pixels, too.
When a picture is printed in a conventional manner in the above mentioned structure, the light transmitted through one frame of a film negative 2 which has been conveyed to and standing still at a printing position is detected by photosensors 8. Then, the filters in the color compensation means 3 are adjusted in response to the picture signals for each of the primary RGB colors and the black shutter 6 is opened to expose a photographic paper 7 with the determined exposure amount.
An image information detecting apparatus 10 comprising a two-dimensional image sensor 11 of area scanning type such as a CCD is mounted at a position near the film negative 2 at an inclined angle with respect to the optical axis LS to facilitate mounting operation. The whole frame of the film negative 2 is segmented into a large number of arrayed pixels for detecting image information. In other words, when predetermined driving signals 101S through 103S are fed from the driving circuit 20 to the image sensor 11, the two-dimensional image sensor 11 is adapted to receive the light transmitted through the film negative 2 on the printing section via the lens unit 12. The two-dimensional image sensor 11 can therefore scan the whole surface of a frame of the film negative 2 along scanning lines SL sequentially by segmenting the whole area into a large number of small pixels 2A as shown in FIG. 4A. After the whole area has been scanned, the output register 103 of the image sensor 11 outputs picture signals PS sequentially, then the picture signals PS are sampled and held by a sample-and-hold circuit 21 and the sampled values thereof are converted by an A/D converter 22 into digital signals DS. The digital signals DS from the A/D converter 22 are logarithmically converted by a logarithmic converter 23 to density signals DN. The density signals DN are input to a write-in control circuit 24 to be stored in a memory in the arrays corresponding to the pixels 2A shown in FIG. 4B and in terms of the density digital values of the film negative 2.
If the digital values for respective pixels of the film negative 2 or the density values for respective pixels with respect to the three primary colors RGB are stored in the memory 25, it is possible to read out the digital values for any particular pixel of the film negative 2 out of the memory 25. If the density values for the respective three primary colors of R, G and B, which are obtained using mosaic filters (not shown) are stored as shown in FIG. 4B, it is possible to read out such values from the memory for processing (which will be described hereinafter) in order to determine the exposure or correction amount for photographic printing in the same manner as in the prior art.
In such a method for measuring the density of the film negative 2, accurate image processing cannot be conducted unless each imaged frame corresponds to an image sensor area or unless the center of each imaged frame coincides with the center of the image sensor 11 constantly; FIG. 5 shows the state where the center SAC of the sensor area SA of the image sensor 11 coincides with the center PAC of the image area PA in a frame of the film negative 2. However, in practice they are often deviated (by the distance .lambda.) from each other even though they remain within the scope of mechanical tolerance or the sensor area SA of the image sensor 11 is inclined from the image area PA (by the angle .theta.). In the prior art system, it is necessary to positionally adjust the attachment of the image information detecting device 10 minutely to cause the center SAC of the sensor area SA to coincide with the center PAC of the image area PA (in other words to make the distance .lambda. zero) and the angle .theta. zero. The attachment and adjustment of the device requires much labor and further, since it needs an additional system for mechanical minute adjustment, it becomes a factor to push up the costs. There has long been awaited a solution for the problem.
In the operation of detecting color image information from a color film negative as shown in FIG. 7, the light of the primary color B out of the light which is transmitted through a film negative 30 is focused on an image sensor 35 by a lens unit 32, and dichroic filter mirrors 33 and 34 are operatively provided in the optical path between the lens unit 32 and the image sensor 35 so that the light of the primary color R which is the light reflected from the dichroic filter mirror 33 is received by an image sensor 37. The light of the primary color G which is the light reflected from the dichroic filter mirror 34 is received by an image sensor 36. When the light from the film negative 30 in three primary color separations is received respectively by one of the three image sensors 35 through 37 (i.e.--sensor 35 is for B, 36 for G, and 37 for R) and stored in a memory in pixels for each of the three primary colors, the sensor address of the image sensors 35 through 37 should be made to precisely coincide with the position of frame images of the film negative 30. For instance, as shown in FIG. 8, if it is assumed that the image sensor 35 of the primary color B has the scope BMA for receiving light, when the scope of the image sensor 36 of the color G is deviated from the scope BMA laterally by a and vertically by b to become situated as RMA, the image sensors 35 through 37 scan different locations on the same film to store them in digital form in a memory. Since these stored images are not aligned positionwise in detection, colors do not come to be in registration to disturb image processing. The positions of two-dimensional image sensors 35 through 37 which receive the image light in three color separation should be aligned to correspond to the same location on images of the film negative 30. The detection areas thereof are aligned by minute positional adjustment in the prior art. This adjustment involves not only cumbersome works but requires also complicated mechanical systems.
Moreover, in the photographic printing system where the direction in the feeding of photographic paper is switched between longitudinal and lateral directions, the sensor area should be adjusted to have its center coincide with the center of image area in both directions.